Last month the United States set a record for the hottest month ever, with July 2012 beating a record set in 1936 by 0.2 degrees. The average temperature recorded in the lower 48 states was 77.6 degrees, beating out every other year since records began in 1895.
The high temperatures weren't just present in July, but continue a trend that began last year. August 2011 to July 2012 is the hottest 12-month period on record. Of the top five hottest Julys on record, three have been recently: this year, 2011, and 2006. The heat has also been hitting the entire country, not just southern states, as has been common in past years.
Scientists have called the temperature hikes significant, and say that global warming is the cause of the unusual around-the-clock heat. Temperatures have remained elevated even during the night, when they typically drop. The fact that the summer has been so dry has also added to the scorching temperatures.
Climate analysis chief of the National Center for Atmospheric Research Kevin Trenberth said the heat is a mixture of both weather and climate change, with the drought causing daytime temperature hikes and long-term global warming causing nighttime rises. Ultimately, though, he said, humans are responsible for the heat wave:
But the fact that the first seven months of the year are the hottest on record is much more impressive from a climate standpoint, and highlights the fact that there is more than just natural variability playing a role: Global warming from human activities has reared its head in a way that can only be a major warning for the future.
Skeptics of global warming say that humans are not causing temperature hikes and extreme weather events like heavy rainfall, hurricanes, and droughts. They argue instead that the weather events of the past century are part of the earth's normal climate cycle, which includes both extreme highs and lows, and are not caused by human activity like carbon emissions, pollution, and deforestation.
Long-time climate-change skeptic Professor Richard Muller recently reversed his views on the topic, writing in the New York Times:
Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I'm now going a step further: Humans are almost entirely the cause.
He said a study showing significant worldwide temperature changes over the past 50 years convinced him of global warming's validity, and that it is likely human greenhouse gas emissions are almost entirely the cause. Yet he also said he continues to be skeptical of wide generalizations made about global warming:
It's a scientist's duty to be properly skeptical. I still find that much, if not most, of what is attributed to climate change is speculative, exaggerated or just plain wrong. I've analyzed some of the most alarmist claims, and my skepticism about them hasn't changed.
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